Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/css/CSSGradientValue.cpp

 /*
  * Copyright (C) 2008 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 34 matching lines @@
 
 void CSSGradientColorStop::trace(Visitor* visitor)
 {
     visitor->trace(m_position);
     visitor->trace(m_color);
 }
 
 PassRefPtr<Image> CSSGradientValue::image(RenderObject* renderer, const IntSize& size)
 {
     if (size.isEmpty())
-        return 0;
+        return nullptr;
 
     bool cacheable = isCacheable();
     if (cacheable) {
         if (!clients().contains(renderer))
-            return 0;
+            return nullptr;
 
         // Need to look up our size.  Create a string of width*height to use as a hash key.
         Image* result = getImage(renderer, size);
         if (result)
             return result;
     }
 
     // We need to create an image.
     RefPtr<Gradient> gradient;
 
@@ skipping 53 matching lines @@
 
     RefPtrWillBeRawPtr<CSSGradientValue> result;
     if (!derived)
         result = this;
     else if (isLinearGradientValue())
         result = toCSSLinearGradientValue(this)->clone();
     else if (isRadialGradientValue())
         result = toCSSRadialGradientValue(this)->clone();
     else {
         ASSERT_NOT_REACHED();
-        return 0;
+        return nullptr;
     }
 
     for (unsigned i = 0; i < result->m_stops.size(); i++)
         result->m_stops[i].m_resolvedColor = textLinkColors.colorFromPrimitiveValue(result->m_stops[i].m_color.get(), currentColor);
 
     return result.release();
 }
 
 void CSSGradientValue::addStops(Gradient* gradient, const CSSToLengthConversionData& conversionData, float maxLengthForRepeat)
 {
@@ skipping 1042 matching lines @@
     visitor->trace(m_firstRadius);
     visitor->trace(m_secondRadius);
     visitor->trace(m_shape);
     visitor->trace(m_sizingBehavior);
     visitor->trace(m_endHorizontalSize);
     visitor->trace(m_endVerticalSize);
     CSSGradientValue::traceAfterDispatch(visitor);
 }
 
 } // namespace WebCore